**Sergey N. Grigoriev, Marina A. Volosova \*, Sergey V. Fedorov and Mikhail Mosyanov**

Department of High-Efficiency Machining Technologies, Moscow State University of Technology STANKIN, Vadkovskiy per. 3A, 127055 Moscow, Russia; s.grigoriev@stankin.ru (S.N.G.); sv.fedorov@stankin.ru (S.V.F.); mmosyanov@yandex.ru (M.M.)

**\*** Correspondence: m.volosova@stankin.ru; Tel.: +7-916-308-49-00

Received: 25 September 2020; Accepted: 26 October 2020; Published: 28 October 2020

**Abstract:** The primary purpose of this work was to study the effectiveness of using diamond-like coatings (DLC) to increase the wear resistance of carbide end mills and improve the surface quality of the processed part when milling aluminum alloy and low-carbon steel. The functional role of forming an adhesive sublayer based on (CrAlSi)N immediately before the application of the external DLC film by plasma-enhanced chemical vapor deposition (PECVD) technology in the composition of a multicomponent gas mixture containing tetramethylsilane was established in the article. The article shows the degree of influence of the adhesive sublayer on important physical, mechanical, and structural characteristics of DLCs (hardness, modulus of elasticity, index of plasticity, and others). A quantitative assessment of the effect of single-layer DLCs and double-layer (CrAlSi)N/DLCs on the wear rate of end mills during operation and the surface roughness of machined parts made of aluminum alloy AlCuMg2 and low-carbon steel 41Cr4 was performed.

**Keywords:** diamond-like coatings; nitride sublayer; index of plasticity; adhesive bond strength; end mills; hard alloy; wear resistance; milling of aluminum alloys; milling of structural steels; surface quality
